Single Switch Controlled Switched Reluctance Machine

ABSTRACT

An improved single-switch control circuit for use in a multi-phase switched reluctance machine is provided. The control circuit includes at least first and second phase windings, a switch, a capacitor, and a diode. The capacitor may have a polarity opposite that of a power source in the control circuit. The first winding may be connected in series with the switch and connected in parallel with a circuit block comprising the second winding. The second winding may be connected in parallel with the capacitor and in series with the diode. In operation, the switch may be used to redirect current from the first winding to the second winding. The capacitor can become charged by the redirected current until it eventually stores enough energy to essentially discontinue current flow in the first winding. Then, the capacitor can discharge its stored energy as a current through the second winding. In this manner, substantially all of the energy from the first winding can be transferred to the second winding.

PRIORITY APPLICATION

Under provisions of 35 U.S.C. §119(e), the present application claimsthe benefit of U.S. Provisional Patent Application Ser. No. 60/955,656,entitled Single Switch Controlled Switched Reluctance Machine, filedAug. 14, 2007, by K. Ramu, which provisional application is herebyincorporated by reference in its entirety.

FIELD OF THE INVENTION

The disclosure herein relates to the field of switched reluctancemachines and, more particularly, to a novel single-switch controlcircuit that controls phase excitations of a multi-phase switchedreluctance machine.

BACKGROUND

Induction motors and universal motors are currently being used in mostapplications requiring constant-speed and low horsepower, mainly becauseof their competitive cost. To replace such conventional motors, researchhas been conducted on single-phase switched reluctance machines (“SRM”)over the last decade. However, prior single-phase SRM machines are notgenerally suitable for high performance applications since they areknown to have some inherent limitations, including low output powerdensity and only a 50% duty cycle of torque generation. They alsorequire an additional component in the form of permanent magnets orauxiliary windings for self-starting.

Because of the known deficiencies of single-phase SRMs, there has beenmore attention paid to multi-phase SRM machines (i.e., having more thanone phase), especially for high torque and/or high-efficiencyapplications. For example, two-phase SRMs may be employed as brushlessmotor drives in variable-speed applications, such as those found in homeappliances and power tools. Two-phase SRMs are particularly desirablebecause of their relative simplicity in design and lower costs tomanufacture. Various types of two-phase SRMs are known in the art, forexample, as described in U.S. Pat. No. 7,015,615, by K. Ramu et al.,issued Mar. 21, 2006.

FIGS. 1A and 1B illustrate one example of a conventional two-phase SRM100. The exemplary two-phase SRM includes a stator 110 having fourstator poles 115 and a rotor 120 having two rotor poles 125. The rotor120 is adapted to rotate around a fixed shaft 130 connected to thecenter of the rotor. A first pair of concentric windings 140, such ascopper coils, are positioned around respective diametrically oppositestator poles 115A. The windings 140 may be electrically connected inseries or in parallel. Similarly, a second pair of concentric windings150 is positioned around respective diametrically opposite stator poles115B. The windings 150 likewise may be connected in series or inparallel. FIG. 1A shows the exemplary two-phase SRM 100 in a firstphase. In this first phase, a current is applied through the windings140 and the resulting magnetic forces cause the rotor poles 125 to alignwith the stator poles 115A. FIG. 1B shows a second phase in which acurrent through the windings 150 causes the rotor poles 125 to alignwith the stator poles 115B. By selectively energizing the windings 140and 150, the first and second phases of the SRM are activated and therotational speed of the rotor 120 can be controlled.

The phase windings in a multi-phase SRM are typically energized by acontrol circuit associated with the SRM. As used herein, a “phasewinding” refers to one or more windings used to activate a single phaseof a SRM or other brushless machine. For example, in FIGS. 1A and 1Beach set of windings 140 and 150 may constitute a different phasewinding in the SRM 100. Most typically, the SRM control circuitcomprises at least one switch per phase winding, for turning on and offcurrent flow in that winding. For example, again with reference to FIGS.1A and 1B, at least one switch (not shown) may be used to control thecurrent flow through phase winding 140, whereas at least one differentswitch (not shown) may control the current flow through phase winding150. U.S. Pat. No. 7,271,564, by K. Ramu, issued Sep. 18, 2007, at FIGS.1-4 illustrates various examples of conventional multi-switch controlcircuits for use with multi-phase SRM machines.

One drawback to conventional multi-switch SRM control circuits is theircost. That is, each switch in the control circuit is typicallyassociated with additional circuitry for controlling its operation. Forexample, each switch may be implemented as a transistor switch havingassociated circuitry for changing the state of the switch, and may befurther associated with other circuit components, such as diodes,resistors, capacitors, etc. In addition, because each switch in themulti-switch circuit may be independently controlled, yet additionalcircuitry may be required to implement separate switch controlstrategies. The added circuitry associated with each of the multipleswitches tends to significantly increase both the cost and complexity ofthe SRM control circuit.

To overcome the disadvantages of multi-switch control circuits,single-switch control circuits have been proposed for use withmulti-phase SRM machines. Previously known single-switch circuitstypically require less circuitry, such as fewer transistor switches anddiodes, than conventional multi-switch control circuits. As a result,the single-switch control circuits can reduce both the cost andcomplexity of the SRM. Such single-switch circuits also have theadvantage that they do not require multiple control strategies forcontrolling multiple switches. Rather, only one switch may be activelycontrolled to trigger multiple phases of the SRM. Various single-switchSRM control circuits are disclosed, for example, in U.S. Pat. No.7,271,564, by K. Ramu, issued Sep. 18, 2007.

FIG. 2 illustrates an exemplary single-switch control circuit 200 thatcan be used in a two-phase SRM. A similar single-switch control circuitis disclosed in U.S. Pat. No. 7,271,564, by K. Ramu, issued Sep. 18,2007, for example, at FIG. 10. The exemplary control circuit 200includes a direct current (“DC”) power source 210 and control circuitry220. As shown, the DC power source 210 may comprise an alternatingcurrent (“AC”) voltage supply 215, a full-bridge rectifier (diodes D1,D2, D3, and D4), and a source capacitor C1. The source capacitor C1 maybe polarized, so as to maintain a substantially DC (i.e., constant)voltage level between its positive terminal (“positive rail”) andnegative terminal (also referred to as a “negative rail,” “common,” or“ground”). Those skilled in the art will appreciate that other types ofpower sources that supply a substantially constant voltage level andcurrent source for use as a DC power source alternatively could besubstituted, e.g., using half-bridge rectifiers or DC voltage supplies,such as batteries.

The control circuitry 220 includes, among other things, a “main” phasewinding L1 and an “auxiliary” phase winding L2, both having positiveterminals electrically connected to the positive rail of the DC powersource 210. The negative terminal of the main phase winding L1 iselectrically connected to the collector terminal of a transistor switchQ1 and to an anode terminal of a diode D5. The negative terminal of theauxiliary phase winding L2 is electrically connected to a positiveterminal of an auxiliary capacitor C2 and to a cathode terminal of thediode D5. In this context, current enters a phase winding through itspositive terminal and exits the phase winding through its negativeterminal. The auxiliary capacitor C2 may be a polarized capacitor havingthe same polarity as the source capacitor C1. For instance, the negativeterminal of the auxiliary capacitor C2 may be electrically connected tothe negative terminal of the source capacitor C1.

The main and auxiliary phase windings may be positioned on respectivepairs of stator poles 115A and 115B (such as the windings 140 and 150shown in FIGS. 1A and 1B). Although the phase windings L1 and L2 may bespatially separated from the control circuitry 220, and in some casesmay be considered to form part of the SRM motor rather than part of itscontrol circuitry, these windings are illustrated in the controlcircuitry 220 for purposes of discussion.

When current flows through the main phase winding L1, a first phase ofthe two-phase SRM can be activated. The second phase may be activatedwhen current flows through the auxiliary phase winding L2. When currentflows through either of the phase windings L1 or L2, i.e., and thus“energizes” the winding, the resultant magnetic energy effects apositive or negative torque in the SRM, depending on the position of therotor 120 with respect to the energized winding. For instance, if therotor poles 125 are rotating toward the energized winding's statorpoles, the change in inductance at the stator poles is positive, thusproducing a positive “motoring” torque that is output by the SRM. On theother hand, if the rotor poles 125 are moving away from the energizedwinding's stator poles, the inductance slope is negative and a negative“regenerative” torque will be produced, i.e., sending energy back to theDC source capacitor C1.

In operation, the transistor switch Q1 directs current through eitherthe main phase winding L1 or the auxiliary phase winding L2 and, assuch, selects a desired phase activation for the SRM. As shown in thisexemplary embodiment, the transistor switch is implemented with an NPNbipolar junction transistor whose emitter terminal is electricallyconnected to the common (ground) potential and whose collector terminalis connected to the main phase winding L1 and diode D5. The transistorswitch is turned ON and OFF by a control signal applied to its baseterminal. Additional control circuitry, such as a microprocessor,digital signal processor, application specific integrated circuit, fieldprogrammable gate array, etc., for supplying the control signal is notshown but will be familiar to those skilled in the art.

When the transistor switch Q1 is turned ON, the DC voltage from thesource capacitor C1 is applied across main phase winding L1 andtransistor switch Q1, causing current to flow through the main phasewinding and transistor switch. The voltage drop across the conductingtransistor switch Q1 is typically negligible compared with the DC sourcevoltage level. While the transistor switch Q1 is turned ON, any currentin the auxiliary phase winding L2 will rapidly decay because theauxiliary capacitor C2 discharges to the DC voltage source capacitor C1,thus causing the voltage at the auxiliary capacitor C2 to eventuallyequal the voltage at source capacitor C1, i.e., resulting in zerovoltage across the auxiliary phase winding L2. The auxiliary capacitorC2 may have a relatively small capacitance compared with DC sourcecapacitance C1 to ensure that it can quickly discharge to the DC voltagesource 210 and attain the DC source voltage level.

In such a conventional single-switch control example, when the currentthrough the main phase winding L1 exceeds a predetermined level, or someother criteria is satisfied, the control signal applied to thetransistor switch may be adjusted to turn OFF the transistor switch Q1.In this case, the current through the main phase winding L1 isredirected through the diode D5, which becomes forward biased when thetransistor switch Q1 stops conducting. The redirected current quicklycharges the auxiliary capacitor C2 above its residual voltage, i.e.,which is equal to the DC source voltage, until the auxiliary-capacitorvoltage exceeds the DC source voltage and causes current to flow throughthe auxiliary phase winding L2.

In some applications, conventional single-switch control circuits mayunderutilize the torque-producing capability of the SRM. For example,there may exist situations where the auxiliary capacitor C2 generates acurrent in the auxiliary phase winding L2 before current has finishedflowing in the main phase winding L1. In such a situation, simultaneouscurrent flow through the main and auxiliary phase windings may reducethe net torque produced by the SRM, because the auxiliary phase windingL2 may produce a positive torque at the same time that the main phasewinding L1 generates a negative torque (or vice versa). A furtherreduction in net torque may result if the current redirected into theauxiliary phase winding L2 circulates back into the main phase windingL1 or into the source capacitor C1. In these cases, the auxiliary phasewinding L2 is deprived from using all of the energy transferred to itfrom the main phase winding L1, thus reducing the amount of torque thatthe auxiliary phase winding L2 can produce in the SRM. Suchrecirculation losses also may increase the commutation time required totransition from the first phase to the second phase.

SUMMARY OF THE INVENTION

The disclosed embodiments provide an improved single-switch controlcircuit for use in a multi-phase switched reluctance machine. To thatend, the novel control circuit includes at least a power source, firstand second phase windings, a switch, a capacitor, and a diode. Inaccordance with the disclosed embodiments, operation of the switchdetermines which one of the first or second windings is energized. Thecontrol circuit may be arranged so that the first winding iselectrically connected in series with the switch and electricallyconnected in parallel with a circuit block comprising the secondwinding. Specifically, the second winding may be electrically connectedboth in parallel with the capacitor and in series with the diode. In thedisclosed embodiments, the capacitor may be a polarized capacitor havinga polarity opposite that of the power source. By orienting thecapacitor's polarity in this manner, when the switch is used to directcurrent through the first winding (e.g., a first phase of the SRM),substantially no current is conducted through either the capacitor orthe second winding. Thus, unlike single-switch control circuits known inthe art, the capacitor accumulates essentially no charge while thecurrent in the first winding is controlled by turning the switch ON andOFF.

Further to the disclosed embodiments, the switch may be used to redirectcurrent from the first winding to the second winding (e.g., a secondphase of the SRM). Because the capacitor stores essentially no residualcharge from the first phase activation, the capacitor can become chargedby the redirected current until it eventually stores enough energy tosubstantially stop the current flow in the first winding. Then, thecapacitor can discharge its stored energy through the second winding,where the discharged current from the first winding is subsequentlyconsumed for torque generation. The diode may ensure that the currentdischarged from the capacitor flows directly into the second winding,and not back into the first winding. In this improved and controlledmanner, substantially all of the energy from the first winding can betransferred to the second winding via the capacitor, thereby maximizingthe amount of torque that the second winding can produce in the SRM.Additionally, the improved efficiency of this novel single-switchcontrol circuit can eliminate recirculation losses in the SRM bypreventing current in the second winding from circulating back into thefirst winding or into the power source.

Advantageously, the disclosed embodiments may find applications invarious multi-phase SRM machines as well as permanent magnet brushlessmachines having two or more phases. Additional advantages of aspects ofthe invention will be set forth in part in the description whichfollows, and in part will be obvious from the description, or may belearned by practice of the invention. The advantages of the inventionwill be realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims. It is to be understoodthat both the foregoing general description and the following detaileddescription are exemplary and explanatory only and are not restrictiveof the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings, which are incorporated in and constitute a part of thisspecification, illustrate embodiments of the invention and together withthe description, serve to explain the principles of the invention.Wherever possible, the same reference numbers will be used throughoutthe drawings to refer to the same or like parts.

FIG. 1A, previously described, is a schematic diagram of a conventionaltwo-phase SRM in a first phase energization;

FIG. 1B, previously described, is a schematic diagram of a conventionaltwo-phase SRM in a second phase energization;

FIG. 2, previously described, is a circuit diagram of a single-switchSRM control circuit that is known in the art;

FIG. 3 is a circuit diagram of an exemplary single-switch SRM controlcircuit that may be used in accordance with a first disclosed embodimentof the invention; and

FIG. 4 is a circuit diagram of an exemplary single-switch SRM controlcircuit that may be used in accordance with a second disclosedembodiment of the invention.

DESCRIPTION OF THE DISCLOSED EMBODIMENTS

The disclosed embodiments provide an improved single-switch controlcircuit for use in a multi-phase switched reluctance machine. In thedisclosed exemplary embodiments, the single-switch SRM control circuitmay include a main phase winding that is electrically connected inseries with a switch and connected in parallel with a circuit blockcomprising an auxiliary phase winding. The main phase and auxiliaryphase windings each may comprise one or more concentric coils positionedon stator poles in the SRM. Furthermore, the main phase and auxiliaryphase windings may be positioned so that any time a current is appliedto either the main phase winding or auxiliary phase winding, a torque(positive or negative) is generated in the SRM. The auxiliary phasewinding may be electrically connected in parallel with an auxiliarycapacitor and connected in series with a diode. The auxiliary capacitormay be a polarized capacitor having a polarity opposite that of a DCpower source in the control circuit. The series-connected diode preventsany current flow from the main phase winding to the auxiliary phasewinding or auxiliary capacitor when the switch is used to direct currentthrough the main phase winding (e.g., a first phase of the SRM).Further, the configuration of the auxiliary capacitor and diode alsoprevents current conduction in the auxiliary phase winding during thefirst phase activation.

The switch may be used to redirect current from the main phase windingto the auxiliary phase winding (e.g., a second phase of the SRM).Because the auxiliary capacitor stores essentially no charge during thefirst phase, the auxiliary capacitor becomes charged by the redirectedcurrent until the capacitor eventually stores enough energy tosubstantially stop the current flow in the main phase winding. Then, theauxiliary capacitor can discharge its stored energy as a current throughthe auxiliary phase winding, where the discharged current issubsequently consumed to produce a torque in the SRM. The orientation ofthe diode may ensure that the current discharged from the auxiliarycapacitor flows directly into the auxiliary phase winding, and not backinto the main phase winding.

In this controlled manner, substantially all of the energy from the mainphase winding can be transferred to the auxiliary phase winding via theauxiliary capacitor, thereby maximizing the amount of torque that theauxiliary phase winding can produce during the second phase.Additionally, the improved efficiency of the disclosed single-switchcontrol circuits can eliminate recirculation losses in the SRM bypreventing current in the auxiliary phase winding from circulating backinto the main phase winding, or flowing into the DC power source, duringthe second phase activation.

FIG. 3 illustrates an exemplary single-switch SRM control circuit 300that may be used in accordance with a first disclosed embodiment of theinvention. The disclosed control circuit 300 includes a DC power source310 and control circuitry 320. For example, the DC power source 310 maycomprise an AC voltage supply 315, a full-bridge rectifier (diodes D1,D2, D3, and D4), and a source capacitor C1. The source capacitor C1 maybe polarized, so as to maintain a substantially DC (i.e., constant)voltage level between its positive terminal (“positive rail”) andnegative terminal (“negative rail,” “common,” or “ground”). Thoseskilled in the art will appreciate that other types of DC power sourcesalternatively could be substituted, e.g., using half-bridge rectifiersor DC voltage supplies, such as batteries.

The control circuitry 320 includes, among other things, a main phasewinding L1 and an auxiliary phase winding L2. The main and auxiliaryphase windings may be positioned on one more stator poles 115 in amulti-phase SRM. In some embodiments, the main phase winding L1 may beconfigured to generate the majority of torque in the SRM, whereas theauxiliary phase winding L2 may be used to assist the main phase windingin its commutation, speed reversal, and/or torque production.

Each of the main and auxiliary phase windings L1 and L2 may consist ofone or more electrically-conductive coils, such as copper-wire coils,that can be connected in series or in parallel within a phase winding.The auxiliary phase winding L2 need not exhibit the same properties asthe main phase winding L1, and may comprise, for example, a differentcurrent-carrying capability, number of turns, volume of copper, and/orcross-sectional area (gauge). More generally, the electrical andmaterial properties of the main and auxiliary phase windings may beselected based on the particular application employing the controlcircuit 300 and cost considerations imposed by that application.Although the phase windings L1 and L2 may be spatially separated fromthe control circuitry 320, and in some cases may be considered to formpart of the multi-phase machine rather than part of its controlcircuitry, the phase windings L1 and L2 are illustrated in the controlcircuitry 320 for purposes of discussion.

According to the first disclosed embodiment, the positive terminal' ofthe main phase winding L1 may be electrically connected to the positiverail of the DC power source 310, and the negative terminal of the mainphase winding may be electrically connected to both an anode terminal ofa diode D5 and a collector terminal of a switch T1. The emitter terminalof the switch T1 may be connected to the negative rail of the DC powersource 310. By way of example, the exemplary switch T1 is shown as a NPNbipolar junction (“BJT”) transistor. However, switch T1 alternativelymay comprise any type of electrical, mechanical, or electro-mechanicalswitch (such as a relay). For example, the switch T1 may be implementedusing at least one transistor switch including, but not limited to, aBJT transistor switch, a metal-oxide-semiconductor (“MOS”) transistorswitch, a field effect transistor (“FET”) switch, an insulated gatebipolar transistor (“IGBT”) switch, etc., or any variation orcombination thereof.

Further to the first disclosed embodiment, a negative terminal of theauxiliary phase winding L2 may be electrically connected to the positiverail of the DC power source 310, and a positive terminal of theauxiliary phase winding L2 may be electrically connected to a cathodeterminal of the diode D5. The positive terminal of the auxiliary phasewinding L2 also may be electrically connected to a positive terminal ofan auxiliary capacitor C2. The auxiliary capacitor C2 may be a polarizedcapacitor having an opposite polarity than the source capacitor C1. Forexample, as shown, the negative terminal of the auxiliary capacitor C2may be electrically connected to the positive terminal of the sourcecapacitor C1.

In operation, the transistor switch T1 can be turned ON and OFF by acontrol signal (or “gating signal”), e.g., applied to the base terminalof the transistor switch T1. To that end, the base terminal may becoupled to gate drive electronics (not shown) including, for example, amicroprocessor, a digital signal processor (“DSP”), an applicationspecific integrated circuit, a field programmable gate array, or anyother processing and/or logic circuitry that provides the control signalto the transistor switch T1. When the switch T1 is turned ON, e.g., in aconducting state, a current flows from the positive rail of the DC powersource 310, through the main phase winding L1, through the switch T1, tothe negative rail of the DC power source. While the transistor switch T1is turned ON, essentially no charge accumulates in the auxiliarycapacitor C2 because of its opposite polarity relative to the sourcecapacitor C1. Further, the orientation of diode D5 prevents current fromflowing through the auxiliary phase winding L2 while the main phasewinding L1 is being energized.

When the current through the main phase winding L1 exceeds apredetermined level, or some other criteria is satisfied, the controlsignal applied to the transistor switch T1 may be adjusted to turn theswitch OFF, e.g., in a non-conducting state. In this case, the currentthrough the main phase winding L1 is redirected through the diode D5 tothe auxiliary capacitor C2. The auxiliary capacitor C2 and diode D5function as a snubber circuit for the transistor T1. Because theauxiliary capacitor C2 has accumulated essentially no charge while theswitch T1 was turned ON, the auxiliary capacitor C2 becomes charged bythe redirected current until the capacitor eventually stores enoughenergy to essentially discontinue the current flow in the main phasewinding L1. The auxiliary capacitor C2 may have a relatively smallcapacitance compared with the source capacitance C1 to ensure that itcan charge quickly.

Substantially all of the energy captured by the auxiliary capacitor C2can be used to generate a current in the auxiliary phase winding L2.Specifically, the auxiliary capacitor C2 can discharge its stored energyas a current through the auxiliary phase winding L2, where thedischarged current is subsequently consumed to produce a torque in themulti-phase SRM. The diode D5 can ensure that the current dischargedfrom the auxiliary capacitor C2 flows directly into the auxiliary phasewinding L2, and not back into the main phase winding L1. In thiscontrolled manner, substantially all of the redirected current isconsumed in the auxiliary phase winding L2, thereby avoiding current inthe auxiliary phase winding L2 from circulating back into the main phasewinding L1 or into the source capacitor C1. Moreover, this single-switchtopology also avoids the need for active control of current through theauxiliary phase winding L2, and hence prevents harmonic-related corelosses in the auxiliary phase winding.

In the first disclosed embodiment, the negative rail of the DC powersource 310 can be used as a common potential for the control circuitry320 as well as for the gate drive electronics (not shown) and any otherassociated computational circuitry (not shown). In this context, and aspreviously discussed, gate drive or gate control electronics refer toany logic and/or processing circuitry for generating the control signalused to toggle (or “gate”) the transistor switch ON/OFF. The otherassociated computational circuitry may include logic and/or processingcircuitry including, for example, a microprocessor, DSP, etc., toimplement a control strategy for toggling the switch T1. Since only asingle common potential may be used in the multi-phase SRM, withouthaving to electrically isolate the DC power supply or the control,gating, or computational circuitry, the relative size, complexity, andcost of the control circuit 300 can be reduced.

FIG. 4 illustrates an exemplary single-switch SRM control circuit thatmay be used in accordance with a second disclosed embodiment of theinvention. The disclosed control circuit 400 includes a DC power source410 and control circuitry 420. For example, the DC power source 410 maycomprise an AC voltage supply 415, a full-bridge rectifier (diodes D1,D2, D3, and D4), and a source capacitor C1. The source capacitor C1 maybe polarized, so as to maintain a substantially DC (i.e., constant)voltage level between its positive terminal (“positive rail”) andnegative terminal (“negative rail,” “common,” or “ground”). Thoseskilled in the art will appreciate that other types of DC power sourcesalternatively could be substituted, e.g., using half-bridge rectifiersor DC voltage supplies, such as batteries.

The control circuitry 420 includes, among other things, a main phasewinding L1 and an auxiliary phase winding L2. The main and auxiliaryphase windings may be positioned on one more stator poles 115 in amulti-phase SRM. In some embodiments, the main phase winding L1 may beconfigured to generate the majority of torque in the SRM, whereas theauxiliary phase winding L2 may be used to assist the main phase windingin its commutation, speed reversal, and/or torque production.

Each of the main and auxiliary phase windings L1 and L2 may consist ofone or more electrically-conductive coils, such as copper-wire coils,that can be connected in series or in parallel within a phase winding.The auxiliary phase winding L2 need not exhibit the same properties asthe main phase winding L1, and may comprise, for example, a differentcurrent-carrying capability, number of turns, volume of copper, and/orcross-sectional area (gauge). More generally, the electrical andmaterial properties of the main and auxiliary phase windings may beselected based on the particular application employing the controlcircuit 400 and cost considerations imposed by that application.Although the phase windings L1 and L2 may be spatially separated fromthe control circuitry 420, and in some cases may be considered to formpart of the multi-phase machine rather than part of its controlcircuitry, the phase windings L1 and L2 are illustrated in the controlcircuitry 420 for purposes of discussion.

According to the second disclosed embodiment, a collector terminal of aswitch T1 may be electrically connected to the positive rail of the DCpower source 410, and an emitter terminal of the switch T1 may beelectrically connected to a positive terminal of the main phase windingL1. The positive terminal of the main phase winding L1 also may beelectrically connected to a cathode terminal of a diode D5. The anodeterminal of the diode D5 may be connected to both a negative terminal ofthe auxiliary phase winding L2 and a negative terminal of an auxiliarycapacitor C2. The negative terminal of the main phase winding L1, thepositive terminal of the auxiliary phase winding L2, and the positiveterminal of the auxiliary capacitor C2 all may be electrically connectedto the negative rail of the DC power source 410. The auxiliary capacitorC2 may be a polarized capacitor having an opposite polarity than thesource capacitor C1. For instance, in the configuration shown, thepositive terminal of the auxiliary capacitor C2 may be electricallyconnected to the negative terminal of the source capacitor C1.

By way of example, the exemplary switch T1 is shown as a NPN bipolarjunction transistor in the control circuit 400. However, switch T1alternatively may comprise any type of electrical, mechanical, orelectro-mechanical switch (such as a relay). For example, the switch T1may be implemented using at least one transistor switch including, butnot limited to, a BJT transistor switch, a metal-oxide-semiconductortransistor switch, a field effect transistor switch, an insulated gatebipolar transistor switch, etc., or any variation or combinationthereof.

The transistor switch T1 can be turned ON and OFF by a control signal(or “gating signal”), e.g., applied to the base terminal of thetransistor switch T1. To that end, the base terminal of the transistorswitch T1 may be coupled to control electronics (not shown), such as amicroprocessor, a digital signal processor, an application specificintegrated circuit, a field programmable gate array, or any otherprocessing and/or logic circuitry that provides the control signal tothe transistor switch T1. Because the emitter voltage of the transistorswitch T1 fluctuates significantly, for example, from toggling betweenthe switch's ON and OFF operational states, the gate drive electronics(not shown) supplying the control signal to the transistor switch T1 maybe electrically isolated from the control circuit 400.

When the switch T1 is turned ON, e.g., in a conducting state, a currentflows from the positive rail of the DC power source 310, through theconducting switch T1, through the main phase winding L1, to the negativerail of the DC power source. While the transistor switch T1 is turnedON, essentially no charge accumulates in the auxiliary capacitor C2because of its opposite polarity relative to the source capacitor C1.Further, the orientation of diode D5 prevents current from flowingthrough the auxiliary phase winding L2 while the main phase winding L1is being energized.

When the current through the main phase winding L1 exceeds apredetermined level, or some other criteria is satisfied, the controlsignal applied to the transistor switch T1 may be adjusted to turn theswitch OFF, e.g., in a non-conducting state. In this case, the currentthrough the main phase winding L1 is redirected to the auxiliarycapacitor C2. Because the auxiliary capacitor C2 has accumulatedessentially no charge while the switch T1 was turned ON, the auxiliarycapacitor C2 becomes charged by the redirected current until thecapacitor eventually stores enough energy to essentially discontinue thecurrent flow in the main phase winding L1. The auxiliary capacitor C2may have a relatively small capacitance compared with the sourcecapacitance C1 to ensure that it can charge quickly.

Substantially all of the energy captured by the auxiliary capacitor C2can be used to generate a current in the auxiliary phase winding L2.Specifically, the auxiliary capacitor C2 can discharge its stored energyas a current through the auxiliary phase winding L2, where thedischarged current is subsequently consumed to produce a torque in themulti-phase SRM. The diode D5 can ensure that the current dischargedfrom the auxiliary capacitor C2 flows directly into the auxiliary phasewinding L2, and not back into the main phase winding L1. In thiscontrolled manner, substantially all of the redirected current isconsumed in the auxiliary phase winding L2, thereby avoiding current inthe auxiliary phase winding L2 from circulating back into the main phasewinding L1 or into the source capacitor C1. Moreover, this single-switchtopology also avoids the need for active control of current through theauxiliary phase winding L2, and hence prevents harmonic-related corelosses in the auxiliary phase winding.

Further to the second disclosed embodiment, relatively small “currentsensing” resistors (not shown) can be added in series with the main andauxiliary phase windings L1 and L2 for monitoring the amount of currentflowing in each of these machine windings. For example, a firstcurrent-sensing resistor (not shown) can be added in series between thenegative terminal of the main phase winding L1 and the common potential.Similarly, a second current-sensing resistor (not shown) can be added inseries between the positive terminal of the auxiliary phase winding L2and the common potential. The voltages across these current-sensingresistors may be fed back to the gate drive electronics (not shown) orother associated control circuitry that use the current-sensingmeasurements to adjust the control signal applied to the transistorswitch T1.

Usually current sensors are expensive in low-cost applicationenvironments and this embodiment uniquely affords the measurement ofinstantaneous phase winding currents in an inexpensive manner andwithout isolation. For instance, if the common voltage for the controlelectronics (not shown) is the negative rail of the DC source voltage,then the sensed currents can be obtained in the form of voltage dropsacross the current-sensing resistors with no need for galvanic isolationbetween the sensed signals and the control circuitry to which they areinput. Likewise, voltages applied across the main and auxiliary phasewindings can be measured, for example, using two sensing resistors (notshown) each connected between a respective one of the main and auxiliaryphase windings and the negative rail of the DC source. Again, thesesensed voltage signals need no isolation for feeding them to the controlcircuitry. Such sensed voltages and currents can be used by the controlelectronics to determine or estimate various SRM machine parameters,such as the rotor position, electrical input power to the phasewindings, and so forth, which in turn may be used to control themulti-phase SRM via the control signal applied to the transistor switchT1.

The foregoing has been a detailed description of possible embodiments ofthe invention. Other embodiments of the invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. For example, while theexemplary control circuits 300 and 400 disclosed herein may not requireadditional self-starting circuitry, such as permanent magnets orwindings (not shown), it is also expressly contemplated that thedisclosed control circuits may be used in conjunction with suchself-starting circuitry. Further, the disclosed exemplary single-switchcontrol circuits may be employed with various multi-phase SRM machines,i.e., having two or more phases, as well as with permanent magnetbrushless machines having two or more phases. In addition, while each ofthe exemplary control circuits 300 and 400 may be used to control atwo-phase SRM, it is also expressly contemplated that a multi-phase SRMmore generally may employ one or more of the exemplary control circuits.For example, a four-phase SRM may include two different single-switchcontrol circuits in accordance with the exemplary embodiments, eachcircuit used to control a different pair of SRM phases.

Although the disclosed exemplary embodiments are hardware-basedimplementations, it is expressly contemplated that at least portions ofthe invention can be implemented in software, including acomputer-readable medium having program instructions executing on acomputer, firmware, hardware, or combinations thereof, as will beapparent to those skilled in the art. Moreover, the disclosedembodiments are not limited to the exemplary circuitry shown in FIGS. 3and 4. Rather, those skilled in the art will understand that theteachings of the invention are consistent with other embodiments thatmay employ other electrical and/or mechanical components, in addition toor in place of, the particular components shown. Accordingly, it isintended that this specification and its disclosed embodiments beconsidered as exemplary only, with a true scope and spirit of theinvention being indicated by the following claims.

1. A control circuit for controlling a multi-phase machine, the control circuit comprising: a power source having an associated polarity; a first winding; a circuit block electrically connected in parallel with the first winding, the circuit block comprising: a diode; a capacitor having a polarity opposite the polarity associated with the power source; and a second winding electrically connected in parallel with the capacitor and electrically connected in series with the diode; and a switch electrically connected in series with the first winding, the operation of the switch determining which one of the first or second windings is energized by the power source, wherein a first phase of the multi-phase machine activates in response to the first winding being energized and a second phase of the multi-phase machine activates in response to the second winding being energized.
 2. The control circuit of claim 1, wherein the switch is associated with at least a first operational state in which the switch is used to direct current through the first winding and substantially no charge accumulates in the capacitor.
 3. The control circuit of claim 2, wherein the switch is associated with at least a second operational state in which the switch is used to redirect current from the first winding to the capacitor until the capacitor has stored enough energy to substantially stop current flow through the first winding, further wherein the capacitor discharges the stored energy as a current through the second winding.
 4. The control circuit of claim 3, wherein the diode is oriented so as to prevent current discharged from the capacitor from flowing back into the first winding.
 5. The control circuit of claim 1, wherein the first and second windings have respective positive and negative terminals, the diode has anode and cathode terminals, and the switch has at least first and second terminals, and further wherein: the positive terminals of the capacitor and second winding are both electrically connected to the cathode terminal of the diode, and the anode terminal of the diode is electrically connected to both the negative terminal of the first winding and the first terminal of the switch.
 6. The control circuit of claim 5, wherein the power source has positive and negative terminals, and further wherein: the positive terminal of the power source is electrically connected to the positive terminal of the first winding and also electrically connected to the negative terminals of the capacitor and second winding, and the negative terminal of the power source is electrically connected to the second terminal of the switch.
 7. The control circuit of claim 1, wherein the first and second windings have respective positive and negative terminals, the diode has anode and cathode terminals, and the switch has at least first and second terminals, and further wherein: the second terminal of the switch is electrically connected to the positive terminal of the first winding and the cathode terminal of the diode, and the anode terminal of the diode is electrically connected to the negative terminals of both the second winding and capacitor.
 8. The control circuit of claim 7, wherein the power source has positive and negative terminals, and further wherein: the positive terminal of the power source is electrically connected to the first terminal of the switch, and the negative terminal of the power source is electrically connected to each of the negative terminal of the first winding and the positive terminals of the second winding and capacitor.
 9. The control circuit of claim 1, wherein the switch comprises a transistor.
 10. The control circuit of claim 1, wherein the first and second windings comprise one or more concentric windings positioned on stator poles in the multi-phase machine.
 11. A multi-phase machine, comprising: a power source having an associated polarity; a first winding; a circuit block electrically connected in parallel with the first winding, the circuit block comprising: a diode; a capacitor having a polarity opposite the polarity associated with the power source; and a second winding electrically connected in parallel with the capacitor and electrically connected in series with the diode; and a switch electrically connected in series with the first winding, the operation of the switch determining which one of the first or second windings is energized by the power source, wherein a first phase of the multi-phase machine activates in response to the first winding being energized and a second phase of the multi-phase machine activates in response to the second winding being energized.
 12. The multi-phase machine of claim 11, wherein the switch is associated with at least a first operational state in which the switch is used to direct current through the first winding and substantially no charge accumulates in the capacitor.
 13. The multi-phase machine of claim 12, wherein the switch is associated with at least a second operational state in which the switch is used to redirect current from the first winding to the capacitor until the capacitor has stored enough energy to substantially stop current flow through the first winding, further wherein the capacitor discharges the stored energy as a current through the second winding.
 14. The multi-phase machine of claim 13, wherein the diode is oriented so as to prevent current discharged from the capacitor from flowing back into the first winding.
 15. The multi-phase machine of claim 11, wherein the first and second windings have respective positive and negative terminals, the diode has anode and cathode terminals, and the switch has at least first and second terminals, and further wherein: the positive terminals of the capacitor and second winding are both electrically connected to the cathode terminal of the diode, and the anode terminal of the diode is electrically connected to both the negative terminal of the first winding and the first terminal of the switch.
 16. The multi-phase machine of claim 15, wherein the power source has positive and negative terminals, and further wherein: the positive terminal of the power source is electrically connected to the positive terminal of the first winding and also electrically connected to the negative terminals of the capacitor and second winding, and the negative terminal of the power source is electrically connected to the second terminal of the switch.
 17. The multi-phase machine of claim 11, wherein the first and second windings have respective positive and negative terminals, the diode has anode and cathode terminals, and the switch has at least first and second terminals, and further wherein: the second terminal of the switch is electrically connected to the positive terminal of the first winding and the cathode terminal of the diode, and the anode terminal of the diode is electrically connected to the negative terminals of both the second winding and capacitor.
 18. The multi-phase machine of claim 17, wherein the power source has positive and negative terminals, and further wherein: the positive terminal of the power source is electrically connected to the first terminal of the switch, and the negative terminal of the power source is electrically connected to each of the negative terminal of the first winding and the positive terminals of the second winding and capacitor.
 19. The multi-phase machine of claim 11, wherein the switch comprises a transistor.
 20. The multi-phase machine of claim 11, wherein the first and second windings comprise one or more concentric windings positioned on stator poles in the multi-phase machine. 